On September 11, 2019, about 1730 eastern daylight time, a Beech K35, N5300E, was involved in an accident at Northeast Florida Regional Airport (SGJ), St. Augustine, Florida. The commercial pilot and pilot-rated passenger sustained minor injuries, and the airplane was substantially damaged. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. According to the pilot, about halfway through the landing rollout on runway 13, the airplane suddenly veered to the right with the engine power at idle. She attempted to correct the turn with left pedal and brake but was unsuccessful. She confirmed with the pilot-rated passenger that the power was at idle. The airplane departed the runway into the grass, struck a berm, flipped over, and came to rest inverted. The pilot further stated that the veer to the right occurred before she could apply the brakes or retract the flaps from the 10° position. The airplane did not have the optional copilot-side brake pedals installed. The airplane’s most recent brake maintenance was performed on January 24, 2019, the same day as the airplane’s most recent annual inspection (when the airframe had accrued a total time of 6,462 flight hours). During that maintenance, the right brake caliper was replaced. The airplane had flown about 60 hours since that time. A Federal Aviation Administration inspector examined the wreckage and the accident site. The examination revealed substantial damage to the fuselage forward of the windscreen, both horizontal stabilizers, and the left ruddervator. A black skid mark was found on the runway that led from the right edge of the runway to the grass. Both wheel brakes and ruddervators and the nosewheel steering functioned normally when the rudder pedals were pressed. The parking brake was found disengaged. Visual inspection of the brake components revealed no mechanical or thermal damage to the brake discs, calipers, or pad material. No hydraulic leaks were visible on any of the fittings or components. Both main landing gear wheels rolled smoothly when the airplane was moved during recovery. The right main landing gear tire had a flat spot worn through the reinforcement cords in the tire tread. Review of a video clip that the pilot provided revealed that the right brake caliper had some play between the two anchor bolts (often called “pins”) and the bushings in the torque plate (the flange to which the caliper is attached). The caliper shifted about the bolts when moved by hand in a twisting motion. The right brake master cylinder was removed and disassembled. The o-rings were intact with no signs of leakage. The return spring was intact. The cylinder exhibited no scoring or signatures of abnormal wear. The poppet valve operated normally. The parking brake actuator valve was sent to the NTSB’s Materials Laboratory for examination. The valve operated normally when compressed air was applied to the inlet port. The valve was then dissembled. The o-ring was intact, and the spring-loaded ball, ball seat, and plunger were undamaged. The plunger moved freely when the actuator arm was moved back and forth.